1. Field of the Invention
The present invention relates to a crankshaft lubrication system including bearings provided with oil grooves, and a crankshaft having journals supported by and turns in the bearings and lubricated with lubricant or oil supplied through the oil grooves. The crankshaft lubrication system is incorporated into, for example, an internal combustion engine.
2. Description of the Related Art
A crankshaft lubrication system disclosed in, for example, JP-U 6-43202 includes bearings lubricated with lubricant or oil pumped out by an oil pump, and a crankshaft having journals supported by and turn in the bearings. Each of the journals is provided with a shaft oil passage through which the oil flows to a crankpin, and a guide groove into which the oil passage opens.
The guide groove extending in the rotating direction of the crankshaft increases the pressure of the oil flowing toward the crankpin, which enables the oil pump to reduce its discharge pressure and reduces power necessary for driving the oil pump.
Part of the oil flowing from the oil groove formed in the bearing supporting the journal into the guide groove leaks through the gap between the bearing and the journal. Therefore, the oil needs to be supplied at an excessively high supply rate to compensate the leakage to ensure proper lubrication of the crankpin. Thus, such leakage has been an obstacle to the reduction of the capacity of the oil pump.
A crankshaft lubrication system disclosed in, for example, JP-U 8-2408 includes a crankshaft provided with plural journals and plural crankpins, and bearings provided with oil passages for distributing the oil pumped out by an oil pump to the journals, in which only some of the journals are provided with shaft oil passage through which the oil is delivered to the crankpins.
Suppose that the journals of the crankshaft are first journals each provided with a shaft oil passage for lubricating the crankpin, and second journals not provided with any shaft oil passage. Then, the oil is supplied at an excessively high supply rate to the second journals, a large amount of the oil leaks through the gaps each between the second journal and the bearing supporting the second journal. Thus, need for compensate the leakage has been an obstacle to the reduction of the capacity of the oil pump.
The present invention has been made in view of such problems and it is therefore an object of the present invention to provide a crankshaft lubrication system capable of reducing the capacity of the oil pump by reducing the amount of leakage of the oil between the bearings and the journals of the crankshaft.
Another object of the present invention is to provide a crankshaft lubrication system capable of reducing oil leakage from journals not provided with any shaft oil passage among journals of a crankshaft and of reducing the capacity of the oil pump by reducing oil supply rate at which the oil is to be supplied to the journals not provided with any shaft oil passage